The long term goal of our research is to investigate the role of smooth muscle myosin heavy chain (SMHC) isoforms in urinary bladder smooth muscle (SM) physiology and pathology. We have shown previously that alternative splicing of a single SMHC gene both at the amino terminus (SM-A and SM-B) and carboxyl-terminus (SM1 and SM2) generate four different SMHC isoforms: SM1A, SM1B, SM2A and SM2B. Urinary bladder smooth muscle expresses predominantly SM1B and SM2B myosin isoforms. Our laboratory recently demonstrated that the NH2-terminal isoform SM-B isoform is an important determinant of the kinetics of urinary bladder smooth muscle contraction. However, the functional relevance of C-terminal isoforms SM1 and SM2 has not been completely understood. To understand the functional significance of the SM1 vs. SM2 isoforms we have recently generated a mouse model that is deficient in SM2 myosin. The female homozygous mice die soon after birth, whereas SM2 male null mice survive up to one month, but die of renal failure and also exhibit severe urinary bladder distension and hydronephrosis. Our hypothesis is that regulated expression of SM1/SM2 isoforms in the bladder body and urethra is critical for the functional maturation of urinary system. Based on the preliminary data, we additionally hypothesize that a switch in SM2:SM1 ratio will affect myosin filament assembly and contribute to bladder dysfunction. Therefore, the major goals of the current proposal are to study how loss of SM2 myosin affects 1) urinary bladder smooth muscle development and maturation in male and female mice, 2) myosin filament structure and distribution within the bladder body and urethra and, 3) the contractile properties of the SM2 null bladder and its response to agonist mediated stimulation. These studies are a major step towards defining the roles of C-terminal isoforms SM1 and SM2 in bladder smooth muscle physiology and will allow us to understand how a switch SM1/SM2 ratio could contribute to pathophysiology of the bladder smooth muscle. PUBLIC HEALTH RELEVANCE: A major goal of this research proposal is to understand the functional role of myosin (contractile protein responsible for force generation) isoforms expressed in smooth muscle .This proposal will examine the role of SM2 myosin isoform in bladder development and function using a mouse model which does not contain this protein.